20 Apr 2021

20 Apr 2021

Review status: this preprint is currently under review for the journal AMT.

Optimal ash particle refractive index model for simulating the brightness temperature spectrum of volcanic ash clouds from satellite infrared sounder measurements

Hiroshi Ishimoto, Masahiro Hayashi, and Yuzo Mano Hiroshi Ishimoto et al.
  • Meteorological Research Institute, Tsukuba, 305-0052, Japan

Abstract. Using data from the Infrared Atmospheric Sounding Interferometer (IASI) measurements of volcanic ash clouds and radiative transfer calculations, we identify the optimal refractive index model for simulating the measured brightness temperature spectrum of volcanic ash material. We assume that the optimal refractive index model has the smallest root mean square of the brightness temperature difference between measurements and simulations for channels in the wavenumber range of 750–1400 cm−1 and compare 21 refractive index models for optical properties of ash particles, including recently published models. From the results of numerical simulations for 164 pixels of IASI measurements for ash clouds from 11 volcanoes, we found that the measured brightness temperature spectrum could be well simulated using certain newly established refractive index models. In the cases of Eyjafjallajökull and Grímsvötn ash clouds, the optimal refractive index models determined through numerical simulation correspond to those deduced from the chemical composition of ash samples for the same volcanic eruption events. This finding suggests that infrared sounder measurement of volcanic ash clouds is an effective approach to estimating the optimal refractive index model. However, discrepancies between the estimated refractive index models based on satellite measurements and the associated volcanic rock types were observed for some volcanic events.

Hiroshi Ishimoto et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-103', Anonymous Referee #1, 27 Apr 2021
    • AC1: 'Reply on RC1', Hiroshi Ishimoto, 03 Aug 2021
  • CC1: 'Comment on amt-2021-103', Dennis Piontek, 12 May 2021
    • CC2: 'Reply on CC1', Hiroshi Ishimoto, 18 May 2021
  • RC2: 'Comment on amt-2021-103', Anonymous Referee #2, 22 Jun 2021
    • AC2: 'Reply on RC2', Hiroshi Ishimoto, 03 Aug 2021

Hiroshi Ishimoto et al.

Hiroshi Ishimoto et al.


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Latest update: 23 Sep 2021
Short summary
Using complex refractive index (RI) models based on new datasets, the accuracy of brightness temperature simulation for volcanic ash clouds in the atmospheric window region was greatly improved. Our results also suggested that the optimal RI model for ash materials can be determined from hyperspectral sounder measurements as well as NBO/T and SiO2 wt. % data obtained from compositional analysis of ash samples under the condition that sufficient RI models are available in advance.